Synthesis of Copper Pyrithione From Zinc Pyrithione and Copper Compound

ABSTRACT

A composition containing unique particles of copper pyrithione wherein greater than 20 wt % to 90 wt % of the particles have a particle size of greater than 10 microns, as determined by laser light scattering using a particle size distribution analyzer, and wherein the particles are flat acicular needle-shaped is described herein. Also described herein is an antifouling paint containing the copper pyrithione and a method of making the composition and antifouling paint.

This application claims the benefit of priority under 35 USC §119(e) toU.S. provisional patent application Ser. No. 61/524,494 filed on Aug.17, 2011, entitled “SYNTHESIS OF COPPER PYRITHIONE FROM ZINC PYRITHIONEAND COPPER COMPOUND”.

FIELD OF INVENTION

The present invention relates to unique particles of copper pyrithioneformed by reacting zinc pyrithione and a copper compound in the presenceof a polymer matrix. The present invention also relates to compositionscontaining such copper pyrithione particles.

BACKGROUND OF THE INVENTION

Ships, fishnets or other underwater structures or equipment tends to beattacked aquatic organisms such as barnacles, mussels, and algae, andthe like. Organisms can grow and multiply and eventually causesignificant problems. For example, in the case of a ship's hull, thegrowth of marine organisms on the hull can increase the frictionalresistance between the hull and water, thus increasing fuel consumptionand reducing the speed of the ship.

One approach to the problems is to coat the surfaces of the structureswith an antifouling coating which contains a “self-polishing” polymer ispresent. “Self-polishing” polymers generally have hydrolysable groupswithin the polymer backbone. Over time, the polymer at the outmost layerof the coating is hydrolyzed and becomes water erodible residue. Thiswater erodible residue is subsequently removed by water, resulting in asmooth, foul free surface. Such action is commonly referred to as a“self-polishing” effect, which continues until the antifouling coatingis removed from the surface to which it is coated. At which time, a newantifouling coating must be placed on the surface. Generally,self-polishing polymers are typically acrylates with metal ester orsilyl ester functionality.

Self-polishing polymers can be used in combination with biocides such ascopper pyrithione to further enhance antifouling performance. Copperpyrithione utilized in the paints typically have relatively smallparticle sizes. Illustratively, EP 1 695 963 B1 discloses that if morethan 20% of the copper pyrithione particles have a size of over 10micron, then it is difficult to disperse the particles in a paint.

Unfortunately, in some formulations, copper pyrithione of a smallparticle size may leach out of the paint film too fast, particularly inwarm water, thus compromising the antimicrobial efficacy of the paint.

Accordingly, there is a need in the paint manufacturing community toprovide a paint that contains adequately dispersed copper pyrithioneparticles having larger particle sizes relative to conventional copperpyrithione particles utilized in the paint. The present inventionprovides an answer to that need.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a composition containingunique particles of copper pyrithione wherein greater than 20 wt % to 90wt % of the particles have a particle size of greater than 10 micronsdetermined by laser light scattering using a particle size distributionanalyzer, and wherein the particles are flat acicular needle-shaped.

In another aspect, the present invention relates to a process for thesynthesis of the unique particles of copper pyrithione described above.The process comprises reacting zinc pyrithione and a copper compoundsuch as copper hydroxide in a non-reactive polymer matrix. The particlesare formed “in situ” resulting in much less agglomeration of theparticles than if made in the conventional manor. Safety in handling isan added benefit because there is no dusting when adding the copperpyrithione into a paint. Further the copper pyrithione particles of theinvention can be easily mixed into a paint because they are alreadypre-dispersed in the non-reactive polymer when they are formed.

In yet another aspect, the present invention relates to an antifoulingcoating composition containing copper pyrithione particles and silylacrylate wherein from 20 wt % to 90 wt % of the particles based on thetotal weight of copper pyrithione have a size of greater than 10 micronsdetermined by laser light scattering using a particle size distributionanalyzer, and wherein the particles are flat acicular needle-shaped. Thecoating composition of the invention contains a higher percentage ofcopper pyrithione particles have a size of greater than 10 micronscompared with convention copper pyrithione particles. The largerparticles will remain in the paint film for a longer time and it isexpected that the coating composition of the invention has sustainedantifouling effect and is particularly beneficial in warm water.

These and other aspects will become apparent when reading the detaileddescription of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a micrograph of the copper pyrithione of the presentinvention.

FIG. 2 is a micrograph of a comparative copper pyrithione.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It has now been surprisingly found that copper pyrithione particleshaving a unique shape and size distribution are formed when zincpyrithione and a copper compound are brought into contact with eachother and reacted in a non-reactive polymer matrix. By “non-reactivepolymer matrix” it is intended to mean a polymer matrix which does notreact with either the zinc pyrithione or the copper compound. Examplesof these polymer matrixes are given below. The formed copper pyrithioneparticles have a flat acircular needle shape. By “flat acircular needleshape” it is intended that the particles have a length, a width and athickness wherein the length is greater than the width and the width isgreater than the thickness. The flat acircular needle shape is a shapethat is distinctly different from that of milled copper pyrithione.

It has also been discovered that anti-fouling paints containing thecopper pyrithione of the present invention have a better resistance tocracking that conventional copper pyrithione.

The copper pyrithione particle have an average aspect ratio, defined asthe length of a copper pyrithione particle divided by the width of thatparticle, in the range of about 5 to about 20 or more. Moreparticularly, the average aspect ratio is in the range of 5 to about 15.Aspect ratio can be determined using any technique known to thoseskilled in the art, including superimposing a micron scale over particlesize images ad comparing the length and width of the particle to thescale. The average aspect ratio is determined by determining the numberof particles provided in the particle size image, determining the aspectratio for each particle and mathematically determining the average ofthe measured aspect ratios for the particle in the image. Images of theparticle may be obtained using a scanning electron microscope.Advantageously, at least 5% of the particles have an average width ofabout 4 to 5 microns and a length of over 20 microns.

In addition to the unique shape, the copper pyrithione particles of theinvention also have a unique size distribution. In one embodiment, from20 wt % to 90 wt %, advantageously from about 25 to about 70 wt %, moreadvantageously from about 30 to about 60% of the particles based on thetotal weight of copper pyrithione have a particle size of greater than10 microns, as measured by laser light scattering using a particle sizedistribution analyzer. For example, the particle size of the copperpyrithione may be measured using a Horiba LA-910 or LA-920 particle sizedistribution analyzer. In addition, the samples of the copper pyrithionemay be sonicated in an aqueous solution before the particle size ismeasured.

The copper pyrithione particles made according to the present inventionare less likely to agglomerate or settle, as compared withcommercially-available milled copper pyrithione. Without being bound byany particular theory, it is hypothesized that the copper pyrithioneparticles are “wet out” by the polymer as they are formed during theprocess of the invention, thus minimizing the agglomeration andaggregation of the particles due to van der Waal forces. In addition,since copper pyrithione particles of the invention are pre-dispersed inthe polymer as they are formed, they are present in a form that issuitable for incorporation into a coating corn position.

Exemplary copper compounds that may be used in the present inventioninclude copper salts, copper carboxylates, copper hydroxide, elementalcopper and combination thereof. Exemplary copper salts include, forexample, copper carbonate, copper nitrate, copper sulfate, copperchloride and mixtures thereof. Exemplary copper carboxylates include,for example copper acetate, copper naphthenate, copper quinolinolate,copper stearate, copper benzoate, copper ethylhexanoate, copperrosinate, and combinations thereof. In one particular embodiment, thecopper compound is copper hydroxide. When copper hydroxide is employedas the copper compound reactant, zinc hydroxide particles are alsoformed. Not wishing to be bound by theory, it is believed that the zinchydroxide particles, to be “wet out” by the polymer particles, thusminimizing the risk of particle agglomeration that otherwise mightoccur.

The form of zinc pyrithione used in the reaction is not particularlylimited. For example, zinc pyrithione can be used in the form of anunmilled wet cake. This provides cost savings for a commercial processbased on the present invention that does not require a milling step.Methods to produce zinc pyrithione are known to those skilled in theart. One example of preparing zinc pyrithione is described in U.S. Pat.No. 4,396,766, which is hereby incorporated by reference in itsentirety.

Accordingly, in one embodiment, the present invention provides acomposition of copper pyrithione particles as described above. Thecomposition may additionally contain a polymer which is non-reactivewith the zinc pyrithione and/or the copper compound. Suitable polymersinclude, for example, silyl acrylates, metal acrylates, such as zincacrylates, copper acrylates, polyvinyl chloride, copolymers of vinylchloride, vinyl acetate, copolymers of vinyl acetate, acryliccopolymers, epoxy, alkyd, polyvinyl alcohol, cellulose ethers, acidfunctional acrylates, chitosan, polyvinyl ethers and combinationsthereof or a non-polymer binder selected from the group consisting ofrosin, rosin derivatives, and combinations thereof.

Advantageously, the polymer is silyl acrylate. In one embodiment, thesilyl acrylate has a number average molecular weight of from about 2000to about 6000. Other suitable silyl acrylates are not particularlylimited and are described, for example, in U.S. Pat. Nos. 6,458,878,4,593,055, 4,898,895 and 4,977,989, the contents of these patents areincorporated herein by reference in their entirety.

It is appreciated that non polymer binders such as rosin and rosinderivatives may also be used. Exemplary rosin derivatives include, butare not limited to, copper rosinate and rosin ester.

In another embodiment, the present invention provides a process forpreparing copper pyrithione particles. The process includes reactingzinc pyrithione with a copper compound in the presence of a non-reactivepolymer matrix.

Typically, the reaction may be carried out in the presence of a solvent.Preferably, the solvent contains at least a water miscible component sothat if wet cake is used, the water from the zinc pyrithione wet cake ismiscible with the polymer solution. If a water free polymer solution isdesired, then dry powder can be used and there is no need for a watermiscible solvent. In some embodiments, the solvent mixture contains awater miscible and a water immiscible component. Exemplary watermiscible component includes, but is not limited to methoxy propanol,methoxy butanol, methoxy-methylethoxy propanol, butoxy ethanol, ethoxyethanol, and porpanol. Exemplary water immiscible component includes,but is not limited to, xylene, toluene, ethyl benzene, naphthas, methylisobutyl ketone, and cumene. Partially water miscible solvents such asmethyl ethyl ketone or butanol may also be used. An exemplary solventsuitable for use in the process of the present invention is acombination of methoxy propanol and xylene. A water miscible solventdoes not have to be used, but is optional.

The reaction can be conducted at room temperature or at elevatedtemperatures and under normal atmospheric pressure. In one embodiment,about one mole of zinc pyrithione is reacted with about one mole ofcopper compound to produce about one mole of copper pyrithione. Thereaction is carried out in a mixture of solvent and the non-reactivepolymer such as the silyl acrylate polymer.

In yet another embodiment, the present invention provides an antifoulingcoating composition containing copper pyrithione particles and silylacrylate polymer described above wherein from 20 wt % to 90 wt % of theparticles based on the total weight of copper pyrithione have a size ofgreater than 10 microns determined by laser light scattering using aparticle size distribution analyzer such as Horiba LA-910 or LA-920, andwherein the particles are flat acicular needle-shaped.

Advantageously, silyl acrylate polymer and copper pyrithione combinedare present in an amount of from about 10% to about 80%, more preferablyfrom about 30% to about 60%, based on the total weight of the coatingcomposition.

The anti-fouling coating composition of the invention may additionallycontain one or more water soluble resins or slightly water solubleresins such as rosin, polyvinyl ether, chitosan, or combinationsthereof. The formulating amount of these resins is preferably within therange of 1-20%, more preferably 4-15%, based on the total weight of thecoating composition.

The anti-fouling coating composition may also include some otheradditives. For example, toxins to prevent hard fouling such as coppermetal, cuprous oxide, copper thiocyanate, zinc oxide, zinc borate,barium metaborate, triphenly boron pyridine, triphenyl boron octidecylamine, tralopyril, chlorfenapyr, tolylfluanid, or dichlofluanid; andtoxins to control soft fouling such as zinc pyrithione, copperpyrithione, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one, 2-methylthio4-tert-butyl amino-6-cyclopropyamino-s-triazine, zineb, ziram,polycarbamate, maneb, chlorothalonil, and any mixtures thereof.

Zinc oxide is typically used in conjunction with cuprous oxide inantifouling paints for the purpose of providing inhibition of hardfouling. However, since zinc oxide converts to zinc hydroxide underalkaline conditions such as in sea water, the present inventor believesthat it is actually zinc hydroxide that is inhibiting the growth of hardfouling. Unfortunately, zinc oxide is typically hard to disperse inpaints, although it must be well dispersed so that the paint is notgritty. This process of dispersing zinc oxide to fine particles in apaint to can take a long time. The present invention overcomes thatobstacle by providing zinc hydroxide “in situ” as fine particles not inneed of further dispersion.

The antifouling coatings according to the present invention can beprepared, for example, by adding resins and/or other toxins to acomposition containing silyl acrylate polymer and particulate copperpyrithione having a large flat particle. The antifouling coating forms adry film when it is coated on the substrate surface by a conventionaltechnique and the solvent thereof is evaporated off at atmospherictemperature or elevated temperature.

The present invention is further described in detail by means of thefollowing Examples. All parts and percentages are by weight and alltemperatures are degrees Celsius unless explicitly stated otherwise.

Experimental

EXAMPLE 1 Preparation of a Composition Containing Self-Polishing SilylAcrylate Polymer and Copper Pyrithione

A. Preparation of Silyl Acrylate Copolymer

To a one liter reaction flask equipped with an addition funnel, a refluxcondenser, a stirrer and a thermometer, were added 368.0 grams ofxylene. The reaction mixture was brought up to 95±5° C. while stirringat low speed under a nitrogen blanket.

The following monomers and initiators were premixed thoroughly in aseparate flask: 180.0 grams of methyl methacrylate, 20.0 grams of2-methyl ethyl acrylate, 200.0 grams of triisopropyl silyl acrylate, and4.0 grams of 2,2-azobis(2-methylbutanenitrile. The monomer/initiatormixture was transferred to the addition funnel mounted on the reactionflask; and was added at a constant rate to the reaction flask over aperiod of 3 hours at 95±5° C. while stirring continuously for anadditional 2 hours.

Next, the addition funnel was charged with premixed xylene (32.0 grams)and t-butylperoxy 2-ethylhexyl carbonate (2.0 grams). This chasermixture was added into the reaction flask drop wise over the course ofone half hour at 95±5° C. The reaction mixture was stirred for anadditional 1½ hours at 95±5° C. thus obtaining the silyl acrylatepolymer.

The molecular weight of the above polymer measured by Gel PermeationChromatography is typically approximately Mw=17,000 and Mn=4700.Viscosity of the silyl acrylate in 50% xylene is typically about 3,000cps (#4 LV spindle at 12 rpm).

B. Preparation of a Composition Containing Silyl Acrylate Polymer andCopper Pyrithione

To a ½ pint mixing vessel was added 93.0 grams of the silyl acrylatepolymer solution prepared in section A. The mixing vessel was placedunder a high speed cowles type disperser with a 1′ blade. The mixer wasturned to 1000 rpm. To the mixing vessel were added 25.9 grams of 60%solids zinc pyrithione wet cake and 26.3 grams of methoxypropanol. Thespeed of the mixer was increased to 2000 rpm. To the mixing vessel, wasadded 1.45 grams of copper hydroxide (58% copper), followed by 10minutes of mixing and succeeding addition of three more batches ofcopper hydroxide (1.45 grams each batch). Once the reaction mixture hadturned a dark green color, 2.50 grams of NH₄OH (29.6%) was added to themixing vessel and the stirring was continued for 30 minutes to provide acomposition containing silyl acrylate polymer and copper pyrithione.

EXAMPLE 2 AND COMPARATIVE EXAMPLE A Microscopic Analysis of CopperPyrithione

Example 2: Microscopic images of copper pyrithione formed from example 1was shown in FIG. 1. Scale on bottom right is 0-50 microns. The SEMshows the copper pyrithione particles of the present invention to beflat acicular needles.

Comparative example A: microscopic images for ACM (air classifyingmilling) copper pyrithione, available from Arch Chemicals, Inc. undertrade name Copper Omadine is shown in FIG. 2. Scale at bottom right isfrom 0-20 microns. FIG. 2.

EXAMPLE 3 AND COMPARATIVE EXAMPLE B Settling Characteristics of theCopper Pyrithione Particles

Example 3: 11% copper pyrithione was prepared from zinc pyrithionepowder and copper hydroxide in situ in a silyl acrylate and xylenesolution The sample was viewed for settling after two weeks.

Comparative Example B: copper pyrithione powder prepared in theconventional manner was dispersed into the same silyl acrylate andxylene solution to a concentration of 11% copper pyrithione. The samplewas visually inspected for settling after two weeks.

A visual comparision of Example 3 to Comparative Example B shows thatthe conventional copper pyrithione has settled more than the copperpyrithione formed in situ., in accordance with the present invention.

To further demonstrate the superior settling characteristics of thecopper pyrithione formed in situ, the dispersions were diluted 50% withxylene so that the viscosity is very low, under 10 cps for both. After24 hours, there is a substantial difference between the settling of theconventional copper pyrithione and that of copper pyrithione formed insitu, in accordance with the present invention Conventional milledcopper pyrithione has settled by 22 mm. In situ generated copperpyrithione has settled only 7 mm in 24 hrs.

EXAMPLE 4 AND COMPARATIVE EXAMPLE C Particle Size Analysis by LaserLight Scattering

Both the conventionally milled copper pyritione (comparative example C)and the in situ generated copper pyrithione (Example 4) particles sizeswere measure by laser light scattering. Measurements were taken withdifferent sonication pretreatments to break up weak agglomerates.Sonication times were 0, 30, and 120 seconds. The results are shown inTable 1. The data show that the in situ generated particles are muchbigger and broadly represented in a bimodal distribution.

TABLE 1 Sonication Average particle Copper Pyrithione time size % □ 5μ %□ 10μ Comparative 0 5.29 49.0 21.4 Example C Comparative  30 seconds5.28 49.0 21.2 Example C Comparative 120 seconds 4.99 52.0 12.9 ExampleC Example 3 0 12.66 36.3 53.2 Example 3  30 seconds 11.32 37.0 52.8Example 3 120 seconds 10.29 37.0 51.5

Stoke's law suggests that all things being equal that smaller sphericalparticles should settle slower in identical liquids. Since the muchlarger particles of the in situ generated copper pyrithione settle muchslower, the conclusion is that the particles are very different fromspherical. The SEM shows the particles to be flat acicular needles. Thelarger needles physically interfere with the settling of the particlescompared to the conventional copper pyrithione.

EXAMPLE 5 Crack Resistance of Paint made with Copper Pyrithione

The longer copper pyrithione particles would be expected to betterreinforce the paint film when compared to the shorter, smallerconventionally milled copper pyrithione particles. To determine this,antifouling paints were formulated from the same silyl acrylate polymer,but with either conventional copper pyrithione added or with copperpyrithione formed in situ by the present invention.

A silyl acrylate polymer solution was produced as in example 1 andpaints were made from this polymer. First, mixtures (dispersions) ofcopper pyrithione and polymer were made, and the paints were made fromthese mixtures. All weights are in grams.

Copper pyrithione dispersion A. Silyl acrylate solution, 50% 100.0 Zincpyrithione 97% 12.50 Cu(OH)₂ 4.16 NH₄OH 1.50

Cu(OH)₂ is added slowly over 80 minutes under the shear of a 1″dispersing blade at 3000 rpm.

Copper Pyrithione Dispersion B. Silyl acrylate solution, 50% 50.0 Copperpyrithione 97% 12.5 Mix for 20 minutes under shear of at 1″ dispersingblade at 3000 rpm. Speed lowered then add; Silyl acrylate solution 50.0

Paints were made from each of the above copper pyrithione dispersions.

Paint A. Silyl acrylate/copper pyrithione dispersion A 30.0 Talc 5.0Cuprous oxide 50.0 Bentone SD-2 0.50

The above ingredients were mixed for 20 minutes at 3000 rpm with 1″dispersing blade then the following components were added:

Disparlon A650-20X polyamide wax 4.00 Xylene 12.0

Mixing continued at 3000 rpm for 5 minutes, lower speed and then thefollowing component was added:

Silyl acrylate copper pyrithione mix A 20.50

Paint B. Silyl acrylate/copper pyrithione dispersion B 30.0 Talc 5.0Zinc Oxide 1.50 Cuprous oxide 50.0 Bentone SD-2 0.50

The above ingredients were mixed for 20 minutes at 3000 rpm with 1″dispersing blade then the following components were added:

Disparlon A650-20X polyamide wax 4.00 Xylene 12.0

Mixing continued at 3000 rpm for 5 minutes, lower speed and then thefollowing component was added:

Silyl acrylate copper pyrithione mix B 18.0

Both wet paints were then applied to separate Leneta charts using a bar(Bird) applicator to produce a wet film thickness of approximately 0.003inches (75 microns). The paint films were allowed to dry for 7 days.Each sample was bent over a ¾ inch mandrel. The films were slowly bentover a 3 second interval over the mandrel. After bending, the surfacesof the paint films were visually examined for cracks. The paint filmfrom the paint made with copper pyrithione of the present invention wasfree of cracking. The paint film from the paint made with conventionallyproduced copper pyrithione showed some degree of cracking.

While the invention has been described above with references to specificembodiments thereof, it is apparent that many changes, modifications andvariations can be made without departing from the invention conceptdisclosed herein. Accordingly, it is intended to embrace all suchchanges, modifications, and variations that fall within the spirit andbroad scope of the appended claims.

1. A composition containing particles of copper pyrithione wherein fromgreater than 20 wt % to 90 wt % of the copper pyrithione particles havea particle size of greater than 10 microns determined by laser lightscattering using a particle size distribution analyzer, and wherein theparticles of copper pyrithione are flat acicular needle-shaped.
 2. Thecomposition of claim 1 wherein from 25 wt % to 70 wt % of the particleshave a particle size of greater than 10 microns.
 3. The composition ofclaim 1 wherein from 30 wt % to 60 wt % of the particles have a particlesize of greater than 10 microns.
 4. The composition of claim 1 furthercomprising a polymer selected from the group consisting of silylacrylates, metal acrylates, polyvinyl chloride, copolymers of vinylchloride, vinyl acetate, copolymers of vinyl acetate, acryliccopolymers, epoxy, alkyd, polyvinyl alcohol, cellulose ethers, acidfunctional acrylates, chitosan, polyvinyl ethers and combinationsthereof or a non-polymer selected from the group consisting of rosin,rosin derivatives, and combinations thereof.
 5. The composition of claim4 wherein the polymer is silyl acrylate.
 6. The composition of claim 5wherein the silyl acrylate has a number average molecular weight ofbetween about 2000 to about
 6000. 7. The composition of claim 6 furthercomprising zinc hydroxide.
 8. An antifouling coating compositioncomprising copper pyrithione particles and a silyl acrylate polymer,wherein from 20 wt % to 90 wt % of the copper pyrithione particles havea size of greater than 10 microns determined by laser light scatteringusing a particle size distribution analyzer, and wherein the copperpyrithione particles are flat acicular needle-shaped.
 9. The antifoulingcoating composition of claim 8 further comprising a water soluble orslightly water soluble resin, wherein said resin is present in an amountof from about 4 to about 15% based on the total weight of the coatingcomposition.
 10. The antifouling coating composition of claim 9 whereinthe resin is selected from the group consisting of rosin, polyvinylether, chitosan, and combinations thereof.
 11. The antifoulingcomposition of claim 8 further comprising an additive selected from thegroup consisting of copper metals, copper oxide, copper thiocyanate,zinc oxide, zinc borate, barium metaborate, triphenyl boron pyridine,triphenyl boron octidecyl amine, tralopyril, chlorfenapyr, tolyfluanid,dichlofluanid, zinc pyrithione,4,5-dichloro-2-n-octyl-4-isothiazolin-3-one, 2-methylthis-4-tert-butylamino-6-cyclopropyam ino-s-triazine, zineb, ziram, polycarbamate, maneb,chlorothalonil, and combinations thereof.
 12. The antifoulingcomposition of claim 8 further comprising zinc hydroxide. 13.-19.(canceled)
 20. The composition of claim 1 wherein the copper pyrithioneparticles are obtained by reacting zinc pyrithione with a copper salt inthe presence of a non-reactive polymer or non-polymer binder.
 21. Theantifouling coating composition of claim 8 wherein the copper pyrithioneparticles are obtained by reacting zinc pyrithione with a copper salt inthe presence of a non-reactive polymer or non-polymer binder.